Filtering illumination for image lift

ABSTRACT

Arrangement for lifting image of checks, with Xenon lamp, Fluorescent lamp or like source of stable-wavelength-output and CCPD Camera means selected to exhibit &#34;close-to-human&#34; spectral response plus a photopic filter, disposed upstream of the Camera and adapted to shift its received image-light spectrum in the direction of that which is optimal for the human-eye.

RELATED CASES

The following U.S. Applications, all filed by the instant assignee onOct. 10, 1989, co-pend with the instant case and are somewhat related:

U.S. Ser. No. 419,574 for "ELECTRONIC IMAGE LIFT",

U.S. Ser. No. 419,560 for "INFRA-RED EXTRACTION FROM ILLUMINATIONSOURCE",

U.S. Ser. No. 419,044 for "RANDOMIZING OPTICAL CONVERTER FORILLUMINATION BEAM",

U.S. Ser. No. 419,572 for "DOCUMENT-IMAGING ILLUMINATION WITHFIBRE-OPTIC INTENSITY ADJUST",

U.S. Ser. No. 419,045 for "PACKAGING OF COMPONENTS FOR IMAGE LIFT".

FIELD OF THE INVENTION

This invention relates to high-speed check processing, and moreparticularly to associated "image-lift" operations whereby an electronicimage of a document is made and stored.

BACKGROUND, FEATURES

Automatic, high-speed check-processing/imaging systems are well known inthe art. Many difficulties and disadvantages of present systems stemfrom how well the imaging-radiation is tailored to the detectors. Sincethe checks can be mis-imaged by poorly matching imaging radiation to itsassociated electronic camera, the result is apt to be errors--e.g.check-images that include optical "noise" or other distractinginformation, or that "miss" meaningful data.

Workers recognize that electronically-stored data ("electronic images")can be processed much quicker, more reliably and less subject to error.But to do so, one must first capture an accurate image, or modifiedimage, of the physical document and convert this into electroniccomputer (EDP) signals. The EDP image-signals can then be manipulated(e.g. be reproduced for visual review, be sorted and distributed, etc.)much more rapidly, easily and reliably than physical documents.

Current systems contemplated for "electronic image-lift" teach using avideo camera by which an operator views the front and back of the actualdocument as desired. Based on what he sees, the operator canelectronically enter document-data into a computer system; e.g., suchthings as check-amount, account number and other data necessary forprocessing document transactions. Such physical viewing islabor-intensive, is subject to error (e.g. from operator fatigue) and issubstantially slower than an automated image-capture arrangement.

Workers are beginning to think of using imaging technology as a way ofimproving document processing, as disclosed, for example, in U.S. Pat.Nos. 4,510,619; 4,205,780; 4,264,808; and 4,672,186. Generally, imaginginvolves optically scanning documents to produce electronic images thatare processed electronically and stored on high capacity storage media(such as magnetic disc drives and/or optical memory) for later retrievaland display. It is apparent that document imaging can provide anopportunity to reduce document handling and movement, since theelectronic images can be used in place of the actual documents.

It would be somewhat conventional to think of document processing with"image capture" using video cameras, with two light sources, one toilluminate each side of a document, plus various lenses to focus lightonto the document. Successive document-images ("image slices") can bereflected from the document, front and back, into respective videocameras. These can convert the optical image into electronic signals;which can then be converted by appropriate circuitry into digital form.But the foregoing would have serious disadvantages; e.g. it wouldrequire two light sources and two camera systems--something expensive toprovide and cumbersome to coordinate.

This invention addresses such disadvantages; e.g. teaching use of asingle, high-intensity, well-cooled light source (cf. high-output xenonbulb, requiring substantially less power than a two-lamp system); andmounting the light source and associated optical components on a singlebase, and under a document transfer track, for ready access (e.g. formaintenance) and for better thermal isolation. Also, the taught systemis modular (e.g. to plug-in to a relatively conventional sorter); itsimplifies service and manufacture using interchangeable,easily-installed components. The system disclosed usesrandomly-distributed fiber optics and electronic image conversion meansin a high speed, automated "image-lift" system; e.g. one capable ofaccommodating the present advanced needs of financial institutions fordocument processing.

An object hereof is to address at least some of the foregoing problemsand to provide at least some of the mentioned, and other, advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated by workers as they become better understood by reference tothe following detailed description of the present preferred embodimentswhich should be considered in conjunction with the accompanyingdrawings, wherein like reference symbols denote like elements:

FIG. 1 is a perspective schematic idealized configuration of an entireDocument Handling System DH apt for using our invention,

FIG. 2 is an idealized perspective of a Document Processor portion ofthis system DH; with FIG. 3 showing portions thereof in side view andvery schematically; and FIGS. 4, 5 showing in partial-perspectivecertain submodules thereof;

FIG. 6 is a block diagram showing functional units of this DocumentProcessor; while FIG. 7 diagrams image-signal flow therein; and FIG. 8is a block diagram in the fashion of FIG. 1, showing a number of suchDocument Processors;

FIG. 9 is an upper perspective view of a portion of an Image-Stationembodiment, with a different view in FIG. 9A and with portions thereofschematically indicated in the plan view of FIG. 10 and theillumination-optics portion thereof very schematically (functionally)indicated in FIG. 11;

FIG. 12 is a diagram indicating functionally, a preferred constructionof a Fibre Optic bundle portion of this embodiment; while FIGS. 13, 13Aare upper perspective views (front and back) of such a bundle, FIG. 14is a schematized front view of an input face of such a bundle; FIG. 14Agives specifications for such a bundle; and FIG. 15 is a diagram in thefashion of FIG. 12 indicating testing of such a bundle;

FIG. 16 is a schematic functional diagram of the imaging-optics portionof this embodiment; related imaging optics;

FIG. 17 is a partial, side-section of the illumination-optics of theembodiment; while FIG. 18 is an exploded diagram of the lamp-housingsub-section thereof; and FIG. 20 is a similar functional diagram of someof this illumination-optics;

FIG. 19 is a similar functional diagram of how some the imaging-mirrorsof the embodiment are packaged; while FIG. 19A is a section of a portionof the Trunnion mirror assembly thereof;

FIG. 21 is a side-section of an Energy-Dump portion of this embodiment;with an upper portion thereof shown in FIG. 22; a plan view of some"vanes" thereof shown in FIG. 23 (and front-view in FIG. 24); while FIG.25 shows the lamp assembly thereof in partial elevation;

FIG. 26 is a partial side view of some illumination optics; while FIG.26A is an enlarged detail thereof;

FIG. 27 is an exploded perspective of a mount casting for elements ofthe embodiment (with elements thereon exploded-away); while FIGS. 28, 29are side sections of this casting; and FIGS. 27A, 27B, 27C show thecasting installed in a Processor;

FIG. 30 is a schematic plan view of such imaging-optics; while FIGS. 32,33 show these elements, selectively and in side-section; and FIG. 31shows the elements in a functional diagram;

FIG. 34 is a plot of lamp intensity vs wavelength, while FIG. 34A plotsspectral response of the embodiment camera elements with that of thetypical human eye; and

FIG. 35 is a plan view of Front and Rear illumination optics, showingthe light-paths; and FIG. 36 is a like showing of part of the FIG. 35assembly.

DESCRIPTION OF PREFERRED EMBODIMENT Exemplary use

Before giving more details of the subject image-lift embodiment, it willhelp to indicate an examplary use-environment in which such anembodiment can be employed. Such is the document handling arrangement weshow in FIGS. 1-8 (called "System DH"). System DH will now be verybriefly summarized. The methods and means discussed herein, willgenerally be understood as constructed and operating as presently knownin the art, except where otherwise specified; likewise all materials,methods, devices and apparatus described herein will be understood asimplemented by known expedients according to present good practice.

In FIG. 1, System DH may be seen to comprise a Document Processor 1-11(also called DP-N) coupled to a Host Computer system 1-19 and one ormore Storage/Retrieval modules (SRM) 1-13. Workers will understand thatdocuments (e.g. checks, etc.) are to be fed into Processor 1-11 andrapidly transported thereby past various processing-stations (e.g.microfilm and imager as described below) to wind-up in one of severalsort-pockets (see FIGS. 2-8). An "Electronic-image" of each document is"lifted" and sent to a designated SRM 1-13 for storage (e.g. on disks,as known in the art). The SRM(s) communicate with Host 1-19 and withvarious Workstations (e.g. one or more Image Workstations 1-15: a PrintWorkstation 1-17). System DH also includes an Encoder 1-18 (e.g. toimprint MICR characters on checks) and related communications andworkstation units.

FIG. 2 indicates sub-units (modules) of Sort/Processor 1-11, includingan image-lift camera module 1-112 and associated electronics submodule1-114 (see FIGS. 4, 5). FIG. 3 indicates this in schematic side-view.FIG. 6 very schematically (blockdiagrammatically) indicates imaging andother functional units; while FIG. 7 schematically indicates how someimage-lift signals are processed. FIG. 8 indicates, schematically, thepossible use of a number of Sort-Processors 1-11 and Storage Modules1-13.

Document images are to be captured at the real-time sorting speed of thedocument processor. For high-speed document processors, the sortingspeed is at least 1800 documents per minute (300 inches a second, trackspeed); lower speed document processors sort documents at approximately1000 (or less) documents a minute (e.g. 150 inches a second, trackspeed). Acquiring electronic representations of documents traveling atthese speeds is a real challenge and requires specialized hardware andsoftware.

Now, we will briefly outline how a preferred image-lift embodimentworks; and thereafter take-up various sub-units thereof in more detail.

Embodiment A, in general

In general, it will be seen that our preferred "image-lift" arrangementis adapted to be incorporated, as a module IL-M, into a high-speeddocument processor, such as Sort Processor 1-11 (see FIGS. 3, 4, 5 andassociated description). Here, the "image-lift" is performed justupstream of the sort-pockets: (e.g. see FIG. 4, camera 1-112 in ModuleIL-M). FIGS. 9, 10 show a portion of the document transport means forModule IL-M (belts BL, BL' cooperate with track-defining guides G, G',between which a document DC is driven past the Front/Rearillumination/imaging stations). For example, see simplified FIGS. 11, 31for a functional showing of an illumination-path, and an imaging-path,respectively; and also see FIG. 10 where each such "imaging station" maybe understood, generally, as sited where the two illumination beams,from illumination-fibre bundles 21, 21', intersect.

The document transport in module IL-M is adapted to move documents pastfront/rear like slits (SL-F/SL-R), or image windows-; these being offsetfrom one another along the transport path T-P (again see FIG. 10 andnote how the Front and Rear dual-beams intersect path T-P at twodifferent points). Associated, respective Front/Rear imaging-pathscapture an image of a document's respective front and rear faces. Thedocument transport system of module IL-M is adapted to translatedocuments, non-stop, past these slits SL at 300 ips (inches per second).Thus, at the respective points of "image-capture", the opposing trackwalls G, G' are broken by the cited illumination/readback slits SL. Eachslit SL is filled with glare-resistant glass to thus keep documents frombending into it, or being snagged thereby [also see front view in FIG.9A].

The documents are translated along this prescribed transport path T-P sothe front and rear images may be captured, in focus (FIG. 35). Thesystem uses a pair of linear-array CCPDs (charge-coupled photo-diodes,e.g. see FIG. 33) as camera means.

The illumination source (see FIG. 11) is preferably a single,high-output, high-intensity xenon lamp X-L (e.g. 1000 watts), encased ina heat sink H-S (e.g. see FIGS. 11, 17) and fan-cooled. Its beam isfiltered by a "hot mirror"/"energy-dump" combination 2-1/E-D (thismirror, or infrared-reflector, 2-1 diverts the IR component to a specialheat-dump E-D). Then, the rest of the beam goes to a beam splitter 2-3,which passes half the illumination to a Corner mirror 2-5 and reflectshalf to an illumination mirror 2-7'. Mirror 2-5 reflects its beam to alike illumination mirror 2-7, which, in turn, diverts its beam (thiswill illuminate the document Rear) through an illumination lens 2-9,onto an associated "Rear fiber-optic bundle" 21. The fibers of bundle 21convert the circular input-beam to an elongate rectangular output-beam(light bar). This "light bar" is projected (focused) through anassociated Rear slit in Track guide G and onto the Rear side of eachpassing document.

The half of the light beam which Splitter 2-3 reflects to mirror 2-7'will illuminate the Front of documents; this beam is focused through anassociated illumination lens 2-9' onto a second "Front fiber-opticbundle" 21' (like bundle 21). Bundle 21' projects a similar "light bar"through its associated Front slit SL-F onto the Front side of passingdocuments.

Thus, the output of each fiber-optic bundle 21, 21' is a narrow,rectangular high-intensity beam of light--thus yielding opposed, offsetillumination beams onto offset Front/Rear slits SL-F, SL-R and onto theFront and Rear of a passing document (see FIGS. 10, 35; note beams fromfiber-optic units 21, 21').

Each beam from fibre bundles 21, 21' is, however, further divided (seeFIGS. 10, 35, 36) using beam-splitters and associated optics to producea "dual-symmetrical-oblique" illumination beam on each side of thedocument (as opposed to a more conventional single beam). We have foundthat such a pair of symmetrical, oblique beams (e.g. ±30° from theNormal is preferred) will reduce or eliminate distortion, shadowing etc.of the captured image that results from such things as creases and foldsin a document--something very important with financial documents whosesurfaces can vary widely and can present imperfections and folds whichdistort or degrade the image (taken by a CCPD). Each set of dualbeams isfocused onto a respective image slit SL to optimize illumination of itsrespective document-side and thus enhance image-capture.

The two illumination-beams are, therefore reflected from a respectiveface of a passing document to yield a pair of (Front, Rear)"image-beams", each being conducted to respective "CCPD camera" (CCPD,CCPD', see FIGS. 30, 32, 33). Each of these rectangular images will beunderstood as emanating from the "document-slice" its slit produces,being taken along the "normal" to the document-face. One of the two likeimage-beams is now described. The image-beam is sent to an"image-mirror" 3-1 (FIG. 31), arranged and disposed to divert the beamdownward (see FIG. 32) to strike a rotatable Trunnion mirror 3-3. Mirror3-3 is mounted on a rotating semi-cylindrical Trunnion 3-30, and divertsthe beam through a special "photopic filter" 3-7, then to an image lens3-5 which focuses it onto the respective CCPD surface. The CCPD convertsthe image into an electrical analog signal which is sent to dataprocessor means for conversion to digital pulses (as known in this art).

Same critical fcators of the foregoing illumination/imaging arrangementare the following:

Mounting angle and optical properties of Beam Splitter 2-3 to ensure a50/50 light distribution (front and rear); adjustability and stabilityof the trunnion mirrors to keep their image-beam centered on their CCPD;adjustability and stability of each image lens to keep its image-beamfocussed on its CCPD; the spectral output of the lamp XL; the positionof each illumination lens 2-9, 2-9' (FIGS. 17, 26), to so dimensiontheir beams onto their fiber-optic bundles as to give "matched" outputbeams of the same, calibrated intensity; the "winding" and randomizedoutput of the fiber-optic bundles, 21, 21'; the optical characteristicsof the "photopic filters"; and the Filter Response of the Hot Mirror andphotopic filters (deviation from a prescribed response will degradeimage quality i.e., color response). These factors should be coordinatedto produce images of satisfactory quality and accuracy, as will befurther discussed.

details of Camera Submodule

Turning to our preferred imaging (camera) module embodiment (cf. 1-110FIG. 2, etc.), note that, in general, the hardware and interfacescomprise: an Image Lift Subunit, an AC Power Distribution Unit, a PowerControl Module, a Lamp power supply, Track components, Internal andExternal interfaces.

The document transport track of the Camera Submodule has physicallyindependent front and rear guide walls. They are made of metal and haveremoveable glass inserts. (The entire front guide wall assembly may beremoved.) The center (glass-in-slit) portion of the walls is named theoptical gate. The guide walls at the optical gate (slit) areapproximately 0.080 of an inch apart (slits).

Light output by each (Fr., R.) Symmetrical Lighting assembly is focusedthrough its optical gate onto the passing document (front, rear).

The guide walls are equipped with a release mechanism that opens themapproximately three inches. The release mechanism consists of anL-shaped handle and a track-open safety switch. Turning the handlecounterclockwise opens the guide wall, turning the handle clockwisecloses and locks the guide wall. If the guide wall is not completelyclosed, the track-open safety switch sends a signal to the AA logic gateon the document processor. The track-open safety switch is locateddirectly to the rear of the guide wall release handle.

The left guide wall has one beam-of-light (BOL) document detector; theright guide wall has two BOLs. The BOLs trace the progress of documentsthrough the Camera Submodule's document transport track.

Each BOL has a light source on one side of the document path and asensor (phototransistor) on the other side of the document path. Thesesensors are aligned with the light source. As documents pass through theBOLs, they interrupt the beam of light. Document detection status isinterpreted by the document processor.

Mechanical drive for the document transport track of the CameraSubmodule is supplied by the document processor through a mechanicalbelt and pulley system. The Imaging Module is the last module before thepocket modules. Because of this configuration, the Imaging Module can beinstalled into an existing DP-N (Unisys) Document Processor. Theaddition of an Imaging Module reduces the number of pocket modules thatcan be driven by the first control module from four to three. With anImaging Module installed, the second control module drives five modulesinstead of four. FIG. 9 illustrates the mechanical configuration of theCamera Submodule document transport track.

The Image-Lift unit performs image acquisition and includes: alamp-cooling fan unit, an electronic camera PWBA assembly, a pair offiber-optic/optic-tower assemblies, with lenses, mirrors, etc. and amount-casting for the latter assemblies.

The Image Lift Subunit is attached to the document transport mount andcontains the mechanics, optics and electronics necessary to acquireimages of documents at the real-time processing speed of the DocumentProcessor 1-11. Images of documents are captured, in real time, as theypass through Processor 1-11 at very high speeds (prefer 300 inches persecond). The Image Lift Subunit, as above-noted, acquires documentimages by illuminating both document sides and capturing an electronicimage of each.

Illumination elements (FIGS. 11, 17)

High intensity light is output by a high-pressure lamp XL thru anaperture S. The light immediately encounters an infrared-removing mirror("Hot mirror") 2-1 which filters-out the infrared component and reflectsit to an Energy-Dump E-D, where it is dissipated as heat (FIG. 11);[Note: excessive infrared can degrade the sensors and interfere withimaging].

Light source XL preferably comprises a 1000 Watt, high-output,commercially-available xenon lamp bulb LS. Bulb-LS (FIGS. 18, 17, 25)preferably draws 32 to 50 amperes at 20 volts (with a voltage rise of 30KV. during initial ignition) and is mounted in a housing HG including animaging-aperture S through which its light output is projected (ontomirror 2-1 etc.) A cooling fan F (FIG. 17) is placed opposite slit S,while the bulb LS itself is surrounded by a heat sink SK (including finsff) of cast aluminum. Heat sink SK defines an inner cylindrical spacesurrounding, and contacting, bulb LS to conduct heat away. The outersurface of SK exhibits radial fins ff which are surrounded by a plasticcontainer C. Cooling air is thrust by fan F across fins ff to exitthrough exit-slots ES disposed all about housing HG, and around slit S.This gives a continuous flow of air for cooling the lamp bulb LS.

The Lamp Assembly XL (refer to FIGS. 17, 18) is in a sheet-metal box HGthat houses the lamp LS, the heat sinks SK and a Lamp Ignition ModuleI-m. The cooling fan F is secured to the cover CV of the box.

The Lamp Assembly and cooling fan are both field-replaceable units. Forexample, if a lamp or Lamp Ignition Module malfunctions, one unscrewsthe cover and replaces the box (and all its contents); one thenreattaches the cover and cooling fan.

Cooling fan F has a rotational sensor that monitors its performance. Ifthe fan fails, lamp LS is at risk of overheating and failing. Inaddition, fan F always turns when the document processor is on, to thusensure cooling of the lamp even if the Imaging Module is powered-off.

The Lamp Assembly is attached to the Image Lift Subunit. Light exitsthrough a hole S in the rear of the Lamp Assembly into the front of theimage lift. This mechanical interface is covered by a cylindricalurethane seal 4-7, which ensures that dust and debris do not enter theImage Lift Subunit (e.g. see FIG. 18).

Lamp LS is a 1000-watt, short-arc, high-pressure (Xenon) device thatrequires 32 to 50 amps of current to operate. The amount of currentrequired is dependent upon the age of the lamp and the intensityrequired of it. (Newer lamps require less current to operate.) Lamp LSdoes not operate correctly with less than 32 amps of current.

The intensity of lamp LS is controlled by Imaging Module softwarethrough the Diagnostic and Transport Interface and Lamp Control PWBAs.As the lamp ages, additional current is supplied to it to compensate forits aging process. The intensity of the lamp is to be thus held constantthroughout its lifespan.

Lamp S is held in place by heat sink assembly SK, which helps dissipatethe heat energy generated. The lamp has an estimated lifetime of 2000hours. (Its life expectancy decreases slightly each time it ispowered-on.) A Lamp Ignition Module I-m (FIG. 18) provides startingvoltage; it produces a 30 kilovolt pulse at approximately 1/2 secondintervals.

FIG. 34 generally depicts the (ideal) spectral output of such a lamp LS,giving intensity vs wavelength.

The infrared energy-dump E-D consists of an enclosure SP with upper andlower sets of blackened metal vanes (v_(u), v_(L) ' FIG. 17) to absorbthe IR. A fan FN is provided at one end of enclosure SP to draw coolingair over vanes v. FIG. 21 rather schematically illustrates thisEnergy-Dump E-D in side view (upper vanes in FIG. 22), showing fan FN atthe rear of enclosure SP, with upper and lower sets vanes (v_(u), v_(L))indicated in phantom (see arrow denoting air-flow over vanes; assume IRbeam from hot-mirror 2-1 enters to impact reflector SR at the front ofSP--see schematic front view in FIG. 24). As indicated in FIG. 23 (aschematized, partial, side-view), upper and lower vanes v_(u), v_(L)face one another, leaving a "convergent-cone" space there-between forbeam-entry. In each set, the vanes are aligned parallel and equi-spaced(e.g. 1/2" apart); they obliquely-face the opposite set, being disposedat 45° to the centerline of SP. Reflector S-R, provided at the front ofSP, diverts the in-coming IR beam into the conical "mouth" between thetwo sets of vanes (v_(u), v_(L)). With the IR component removed, theremainig beam spectrum will be "safer" (cooler) and more closely"matched" to the response of the CCPD.s (see below).

The resultant "cooled" light beam is passed from hot mirror 2-1 to abeam splitter 2-3 (FIG. 11); i.e. a partially-metallized mirror thatreflects one-half the beam and passes the other half. Between beamsplitter 2-3 and hot mirror 2-1, a safety shutter Sh is preferablyprovided for selective interception of the light beam, whereby to divertthe entire beam to Energy-Dump E-D in the event of emergency shut-downor for maintenance purposes (the beam from lamp LS is powerful enough,when focued, to cause injury to the human eye; note: Xenon lamp LS ispreferably kept lit at all times during system operation; lamp lifedegrades as a function of the number of ON/OFF cycles). Shutter sh ispreferably mounted to be pivoted down (as shown), when activated, and issufficiently reflecting to so direct the entire beam to E-D (toreflector S-R thereof--see FIG. 17).

Beam splitter 2-3 thus develops a pair of like illumination beams, a"Front beam" sent to the front side of the document, and a "Rear beam"to the back side. Thus, from splitter 2-3, one beam is reflected toFront-illumination mirror 2-7', while the other (the thru-beam) goes toa Corner Mirror 2-5. (FIGS. 11, 17, 20). Mirror 2-5 diverts its beam toa second (Rear) illumination mirror 2-7. Illumination mirrors 2-7, 2-7'are essentially identical; each diverts its beam upward through arespective illumination lens 2-9, 2-9' (these are identical),and--according to a feature hereof--they can (adjustably) focus theappropriate beam-size (amount of light) on the entry-aperture of theirrespective fiber-optic bundle thereby regulating the amount of lightemitted at bundle output (e.g. see FIGS. 13, 35, 13A).

That is, rather than reducing lamp-power/intensity (e.g. via apotentiometer controlling lamp-current) as would be more conventional,we prefer to move these Lenses 2-9, 2-9' toward or away from theirrespective fiber bundles 21, 21' and by so adjusting focus, adjust and"match" their beam intensities, quite easily and inexpensively (e.g. see2-9 in FIG. 26, where such shifting is indicated in phantom). Asdiscussed later, each fibre bundle 21, 21' is adapted to receive arelatively circular input light-beam and to output it, reshaped and withsegments redistributed, as an elongate "bar" (rectangular beam) of lightwhich is quite uniform along its length and (narrow) width.

Thus, as illustrated very schematically in FIG. 14 (front view of a"circular" fibre-bundle input-face or entry-aperture 21-1F, with 21-OPrepresenting the outer periphery of this input-face), workers willappreciate that simply shifting such a lens 2-9, 2-9' to change itsfocus, one can quite simply change the beam-diameter on anentry-aperture 21-F (changing intensity at output face 21-E; yet do soproportionately),--while still keeping the output "bar" quite uniform inintensity etc. (e.g. an input beam twice the size of maximum aperture OPwould yield about 1/2 the output intensity). Thus, for example "maximum"beam intensity can correspond to an input beam-diameter matching that ofthe full entry-apertures; then output intensity can be adjusted-down bysimply changing lens focus to enlarge this beam's input-diameter and soreduce the amount of entry light. And the two (Front, Rear) output"bars" can be "matched" in intensity quite easily and inexpensively(e.g. a less-desirable alternative is the well-known, expensive,delicate "iris" structure used in consumer-type cameras). Thus,according to this feature, one can calibrate and match the twoillumination intensities by simply adjusting each focus-lens onto itsfibre bundle entry-aperture. And so, for calibration ofillumination-intensity, each beam of light focused on its fiber bundleis regulated according to its lens-focus. As mentioned, eachentry-aperture 21A (of a fiber-optic bundle) is relatively circular(e.g. diam. of 0.70"), while each outputaperture thereof is arranged toprovide an elongate rectangular beam (bar of light), sufficiently highto span, and illuminate, the contemplated slit-height/document-height(e.g. 5.25" height "by 0.075"" width is found satisfactory). Eachoptic-fiber bundle is arranged to receive its respective input beam atits circular entry-aperture; and, the fibers are fanned-out, and"randomized", along their length--to be quite uniformly and randomlydistributed along the rectangular output (exit-aperture). This convertsthe input circular beam to a rectangular output beam spanning itsrespective slot (vertically and horizontally). Interestingly, bar-sizedoesn't change as a lens is focused/defocused because of this"randomization".

Thus, as a feature hereof, the optic fibers of each bundle are"inter-leaved" so that their output is "randomized", to yield lightevenly distributed along across a respective slit. That is, as indicatedfragmentarily, and very schematically in FIGS. 12, 15, fibers arearrayed from circular entry-aperture A to rectangular exit-aperture B soas to randomly and evenly distribute light along exit aperture B. Forexample the fibers at the center of entry-aperture A (where intensitymay be maximal) might be distributed uniformly along exit aperture B.Similarly, fibers (any number) at the periphery of A (where intensitymay be a minimum) will be distributed uniformly along B, yet in randomfashion (e.g. see FIG. 14A giving illustrative specification for 21).

Such randomization can be achieved by arraying a first bunch of fibersin a layer along the length of aperture B, then gathering this "bunch"into a "first cluster" at aperture A--and then repeating this manytimes, with each successive cluster placed at a different spot incircular entry-aperture A, until the appropriate aperture-B-thickness(width) is built-up.

FIG. 15 very schematically illustrates the kind of results that suchrandomization should achieve. Here, a fibre bundle 21 will be understoodas depicted with circular entry aperture A and rectangular exit-apertureB. Now, with ambient (or other reasonably good) illumination on B, oneplaces a pencil P (or other narrow light-obstruction, as P-10) acrossany part of B, at random, and observes the effect at A. Where A willnormally exhibit a dull white "glow", the obstruction should produce a"sprinkled-pepper" effect (as in FIG. 15), with a few tiny black "dots"(dark points) sprinkled relatively uniformly across A. Then, successive"blockings" at any other points along B should yield a similar effect.What should not appear at A are relatively large opacities, or a verynon-uniform distribution of black dots.

two dual, Anti-Shadow illumination-beams

Each Symmetrical (Front, Rear), illumination assembly (e.g. FIG. 36 forFront-illumination) divides the light (again) into two equal portions;these portions to be focused onto (their side of) the document intandem, from opposite 30 degree angles. This ensures that a document isevenly illuminated from two angles. For example, otherwise if thedocument has creases, those may cause a shadow which could compromisethe output image. Illuminating each side of the document from twosymmetric opposing 30-degree angles reduces the possiblity of suchshadowing effects.

Each such Symmetrical illumination assembly thus shines its twolight-bars onto the document through an "optical gate" (slit) at ±30degree angles to compensate for document imperfections and provide moreuniform document illumination. The embodiment that provides these two"dual-symmetric-oblique illumination beams on each side of a documentwill now be further detailed. Since Front-side illumination-optics areessentially identical to those for the Back-side, only the Front-sidewill be detailed (see FIGS. 35, 36).

Here, the "elongate rectangular beam" (light-bar) output from the Frontfiber-optic bundle 21' goes to a respective beam splitter (14-1' in FIG.36), where 50% of the light-bar is reflected and 50% is transmitted, sothat two beams are presented on each side of the Front slit. One ofthese beams goes to a cylindrical plastic convex lens (e.g. 14-5') thatfocuses its beam through the slit and onto the "document image plane"I-P (i.e. the locus of document-passage). The companion beam goes thru adifferent cylindrical plastic convex lens 14-3' to a mirror 14-7' whichdirects it onto the same point of the "document image plane"--but doesso from a symmetrically-opposite angle (so the beams converge at ±30°from the "normal" to plane I-P; see "normal" OCL). This is done viaadjustable back-mirror 14-7' which can be set at the appropriate angleto so direct its beam onto "image plane", I-P at the same point [thruimage-slit in guideway].

Each such Front/Back optics system is identical and "symmetric", sothat, on the Front and Back side of the document, dual, converging beamsimpinge on their slit and on "image plane" IP--the Front slit beingoffset from the Rear. We have found that so projecting dual illuminationbeams at these ±30° angles provides optimal light intensity and imageclarity. As workers know, maximum illumination intensity is typicallyalong the "normal" to a document (i.e. the perpendicular to itsplane)--but, unfortunately, this is also where glare is a maximum; alsothis is where it is most desirable to capture an image. We find that"anti-shadow" illumination is best directed at about 45° to thedocument--but this angle gives an intensity-level that is usually toolow and inefficient (cf. reflected intensity falls-off sharply as onemoves away from the "normal"); so we prefer to accept less than optimalanti-shadowing as a trade-off to increase intensity to a moresatisfactory level--and we have found that, for embodiments like this,opposing angles of ±30° (±5° ) are surprisingly good.

"Image plane" I-P will be understood as (e.g. FIG. 35) defining thelocus of both the front and rear sides (close enough) of a document asit is being read at the two offset "imaging sites" along the documenttransport track. Each such "site" is defined by a respectiveslit-opening SL in the guides, covered by glare-resistant glass andoffset from the other slit by about 0.445 inches. It is important thatdocument location be closely controlled; i.e. for optimum focus andminimal image-distortion (due to Front-to-Rear movement of a document inthe track), the document should be restrained within ±0.045" of nominaltrack-centerline (i.e. intersection of dual, converging beams). Giventhis, the images produced by the two Front/Rear illumination beams canbe captured with uniform balanced illumination. Light intensity isoptimum where each (FR, R) set of dual converging beams intersect, andfalls-off sharply as one moves away from this intersection.

The Front "image point" (slit) is offset from that in the Rear by aspacing (e.g. 0.445 inches in the preferred embodiment) sufficient toavoid interference between beams (e.g. "back-light" from oneillumination-beam could pass thru the thin paper document and interferewith illumination-imaging on the opposite side.) System electronicsprocesses the analog signal from the CCPD detector. A Front CCPDcaptures the image on the front and a Rear CCPD captures that on theback side of the document; and appropriately times and records thesignals received so that the images recorded for the front and rearsides are properly coordinated and are identifiable (as a pair) forprocessing and storage.

System calibration and "illumination-set-up" consist in adjusting theillumination lenses 2-9, 2-9' and mirrors 2-7, 2-7' (FIG. 11) to directand focus the desired (circular) beam-size onto the circularinput-aperture of each fiber-optic bundle 21, 21'; then adjusting theFront and Rear mirrors 14-7, 14-7' (FIG. 36) to focus the two respectivepairs of oblong illumination beams (thru a resp. slit) so that each pairmeets at a common point along the "document image plane" I-P.

Having described the "path of illumination", we now turn to the"image-lift" paths; i.e. the optical paths of images from the front andthe rear sides of the document (these are symmetric, and essentiallyidentical). One side will be described in detail, with the understandingthat the essential elements and description are the same for theopposite side.

image-path (FIGS. 16, 30, 31, 32, 33):

FIGS. 31, 16 very schematically and simply summarize the image-path(both Front and Rear use essentially the same elements). Thus, when adocument portion (passing a respective slit) reflects the illuminationto an image-mirror 3-1, it reflects it (down) to a rotatable Trunnionmirror 3-3. Mirror 3-3, in turn, reflects it to a respective CCPD, via aphotopic filter 3-7 and image-lens 3-5. Mirror 3-3 can be rotated tocenter its beam on its CCPD.

Thus, the Front/Rear dual illumination beams (from a respectivefiber-optic bundle, after splitting) will be understood as impacting thepassing document at offset points, each illumination beam beingunderstood as reflected directly-back (i.e. normal to plane I-P) to arespective image mirror 3-1, 3-1', titled at 45 degrees from plane I-P(FIGS. 16, 31, 32). Each image mirror 3-1, 3-1' (Front, Rear) re-directsits reflected beam vertically down to a rotatable "plane trunnion"mirror 3-3, 3-3', which diverts its beam, aiming it to be centered onthe associated CCPD via a filter 3-7, 3-7' and a focusing lens 3-5,(3-5'). Each trunnion mirror 3-3, 3-3' is mounted in a housing 3-30 (seeFIGS. 19, 19A, 31) which allows it rotational adjustment, withoutdisassembly, to adjust image position (center it) on its CCPD.

As shown in FIG. 19A, the adjustment mechanism consists of twoset-screws TS-1, TS-2 which contact seats cut-out in the ends of thesemi-cylindrical mirror-casing 3-30, each being threadably seated in thehousing. More particularly, the trunnion cylinder 3-30 (FIGS. 19, 19A)is rotationally restrained between the tip of an adjusting set screwTS-1 and a coil spring T-SP (a music-wire coil compression spring lodgedin housing OT to contact 3-30 restrainingly, being held in place by amachine screw TS-3). Rotation of set screw TS-1 will cause trunnioncylinder 3-30 to rotate about its axis against the force of spring T-SP.Once the trunnion mirror 3-3 is correctly located, a locking set screwTS-2 is tightened to lock the adjustment.

Each trunnion mirror 3-3, 3-3' thus diverts its image-beam horizontally,along a path essentially parallel to the documentpath, through a"photopic" filter 3-7, 3-7" (See FIG. 31) and then through image lens3-5, 3-5' which focuses the beam onto the associated CCPD (CCPD'). Thephotopic filters 3-7, 3-7' are described later; each comprises a planeglass plate with, multi-layers of thin dielectric film, superposedthereon. This series of optical coatings is especially formulated toshape the spectral response of the system as desired. The output fromeach filter thus tailors the image spectrum and conditions it(approximately as shown in FIG. 34-A) to approximate the response of thehuman eye; here, the light from a Xenon light source LS is "shifted-red"by approximately 25 nm to give this result.

Each image lens 3-5 (3-5'), following its filter, is made adjustable soas to focus its beam onto the surface of its CCPD; and, each can beadjusted for "Coarse" and "Fine" focus by means of a rotating-cam,driving in a slot of the Tower housing OT (see FIG. 26-A).

Lens 2-9 in FIG. 26 is illustrated in detail in FIG. 26A. An eccentriccam 26-C engages in a slot on top of the image lens holder 26-H.Rotation of cam 26-C will cause the image lens holder 26-H to moveleft/right by ±0.025" (the "throw" of the eccentric section of the cam).If more adjustment is required (±0.125"), the screws (not shown)securing the adjuster body 26-B may be loosened and the entire adjusterbody, eccentric cam and lens holder moved back and forth.

For the "image-lift-path", "set-up" procedure consists in rotating eachtrunnion mirror 3-3, 3-3' (e.g. see FIG. 31) to center its beam on itsCCPD; then adjusting each associated image lens to focus its beam ontoits respective CCPD.

The (two) Electronic Camera PWBAs each include a linear CCPD sensingarray, with video signal amplification, clock generation, clockbuffering, and power distribution circuits. The selected CCPD("charge-coupled photo-diode") device will have a response analogous tothe retina of the human eye when combined with the response of thephotopic filter; this is a critical component of the system. In thispreferred embodiment, a pair of like "Reticon RL-1288" linear-array,silicon chips (with 1024 photodiodes) are used. The photodiodes arearranged and positioned to image the "vertical line" reflectedimage-beam from a document. Each like associated image lens 3-5, 3-5'gives magnification, as adjusted, to produce 0.005 inch-high pixels onthe surface of their associated respective document planes I-P. EachCCPD diode array is subdivided into eight segments; each photodiodeelement of the array converts light reflected from the document intoanalog voltage values. The converted electron-charge on the photodiodesis transferred to an analog shift register within the chip when atransfer pulse is applied (not shown, but well known in the art). Theodd and even numbered pixels of each segment are output separately. Thesensing array outputs a representation of the scanned document assixteen analog signals; each signal amplitude corresponds to a pixel'sgray level. The Electronic Camera PWBA also outputs synchronization(clock) signals and identification signals (front, rear sensing arrays).

We have determined that an optimal system response for the lightimpinging on such CCPD.s (for our image-capture purposes--factoring-inthe lamp, filter and CCPD used) should approximate the sensitivity rangeof the human eye. This is indicated in the spectrum of FIG. 34-A. Thespectral output of our selected Xenon lamp LS is fairly flat over therange 450-750 nm.; while peak human-eye spectral response is about 550nm.

We find--somewhat surprisingly-that introducing "photopic" filters, asdescribed, helps greatly to improve Blue-on-Blue contrast (i.e. contrastof blue-ink etc. on a blue background, as many checks etc. willexhibit).

Thus, we introduce filters 3-7, 3-7', which, when combined with thespectral sensitivity of the CCPD detectors, yield an overall systemresponse closely matching that of the human eye, with actual systemresponse shifted 25 nm toward the red end of the spectrum. We have foundthat such a shift improves the response of blue inks on bluebackgrounds, and, to a lesser extent, blue/green and green inks onsimilarly colored backgrounds. Experience has shown that this wavelengthshift is very effective for purposes of our instant document processing.

Our "system Response" should therefore be "photopic" and shouldapproximate the response of the human eye [we are imaging documentswhich are to be "read" by the human eye and are made up of inks andmaterials visible to the human eye]. Without this "spectral shaping"--bythe filter-of the light incident on our CCPD detectors, our system would"read" documents rather differently than the eye does. [e.g. it would"see" in the infrared and would interpret color contrast ratherdifferently; but it is imperative to maintain proper, "human" colorcontrast when it comes time to reproduce the images for human use.]

FIG. 31 (see also FIG. 33) very schematically and functionally,illustrates the "imaging-path"; i.e. the path of the image reflectedfrom (a slice of) the passing document to a respective (Front or Rear)CCPD. Thus, the image will be understood as reflected from theslit-illuminated part of document doc moving along image-plane I-P, to arespective image mirror 3-1 (3-1' on other side); thence to a respectiveturnnion mirror 3-3 (3-3'); thence to its CCPD via respective "photopic"filter 3-7, 3-7' and focusing lens 3-5, 3-5'.

Imaging Process Recapitulated (FIGS. 31, 33 described for Front side;Rear side the same):

Light reflected from the front "slice" of the passing document isdirected to an "optical tower" (Front tower, OT, Rear Tower OT', seeFIGS. 32, 33 19) housing an assembly of mirrors. The light entering eachoptical tower is reflected down by an Imaging mirror 3-1, to a Trunnionmirror 3-3 below the transport level. Each Trunnion mirror swivels on adowel or pin (see 3-30) and can be set (rotated) to center its beam onits CCPD (see FIG. 19A also). Thus, Trunnion mirror 3-3 diverts itslight 90° to related "photopic" filter 3-5, which ensures that theoptical system's spectral response is optimized for the CCPD, and betterapproximates human-eye response [each photopic filter is located at thebase of its optical tower.]

Each image reflected by the trunnion mirrors passes through thesefilters on its way to the CCPD sensing array. After passing through thephotopic filter, the image is focused onto a respective charge-coupledphoto-diode (CCPD) sensing array (see "Electronic Camera PWBA" orprinted circuit board assembly) by an associated Imaging lens 3-5.

Thus, as a document passes through the Camera Submodule, an intensevertical stripe of filtered light is focused on each side, to bereflected from the document to a respective CCPD sensor mounted on anElectronic Camera PWBA.

The Electronic PWBAs convert the light so reflected from the documentinto analog voltages, amplify these and send them to an Electronics GateSubmodule for Analog/Digital conversion, processing, compression, andeventual transmission to temporary storage [cf. the images are sent to aStorage and Retrieval Module SRM for subsequent retrieval by anapplication program--see 1-13, FIG. 1]. FIG. 34A gives the spectrum oftotal system spectral response (i.e. output from CCPD, factoring-ineffect of lamp, optics and filter, etc.).

optic elements, recapitulation

Preferred specifications for some optical elements described above willnow be given. The CCPD sensing arrays preferably consist of 1024photodiodes aligned, in one dimension, to image a vertical line of thedocument. The array is subdivided into eight segments, with eachphotodiode converting its portion of the image to an analog voltage (cf.light-induced charge accumulated on the photodiode). This is transferredto an analog shift register within the chip when a transfer pulse isapplied (not shown, but well known in the art). The odd- andeven-numbered pixels of each image (diode) segment are outputseparately, thus, each CCPD sensing array outputs a representation ofeach scanned document "slice" as sixteen analog signals, with theamplitude of each signal corresponding to its pixel's "gray level". TheElectronic Camera PWBA also outputs synchronization (clock) signals andidentification signals (front or rear sensing arrays).

The imaging module 1-110 incorporates several different types of lensesand mirrors. Thus, illumination lenses (2-9', 2-9 FIG. 11, which focuslight onto a respective fiber-optic bundle 21, 21'), are preferably 75millimeter (diameter), plano-convex lenses with a focal length of 150millimeters. Imaging lenses 3-5, 3-5' (FIGS. 16, 13, which accept lightreflected by the document and focus it onto a CCPD sensing array) aref2.8, high-resolution lenses with a focal length of 50 millimeters.

"Maximum reflectance" mirrors (front-surface mirrors with 99 percentreflectivity) are preferably used as: corner mirror, 2-5 (FIG. 17),Front and Rear illumination mirrors, 2-7, 2-7', (FIG. 11) imagingmirrors 3-1, 3-1' (FIG. 32) and trunnion mirrors 3-3, 3-3'.

Workers will recognize that, instead of the preferred "linear" siliconCCPD.s; in some cases Gallium CCPD.s may be used, and/or two-dimensionarrays--or even "Camera tubes". Workers will also recognize that thereare special advantages to using focus-adjustment to vary beam intensity(cf. adjust lens, vary beam-size on fibre-optic input-face)--notably,that this involves no wavelength-shift, as with more conventionalmethods. For example, it is common, with an incandescent lamp, to changethe filamentheating input-current to vary light intensity--unfortunatelythis also shifts the wavelength spectrum of the light, giving obviousproblems to a CCPD or other "camera" means (similar problem with halogenlamps). So, workers may prefer our focus-adjustment of intensity asbeing unusually "wavelength-stable".

Xenon lamps (gas-discharge) are similarly "wavelength-stable" when theirintensity is varied; fluorescent lighting is almost as "wave-lengthstable", but yields somewhat less-intense light, and this would be aless-preferred alternative.

single-casting mount

We prefer to mount illumination-optics, and the heat-producing lamp andits energy-dump, well below the transport array (platform, guides,belts, etc.) to enhance safety, ease of heat rejection, ease of assemblyand ease of efficient servicing. By contrast, it would be moreconventional to mount these items on the transport platform. Thus, asseen in FIGS. 27, 28, 29, the entire image-lift arrangement is modular,and is mounted on a single main casting M-C which is affixed (bolted) toa base plate BP (FIGS. 28, 29, 9) which carries the document-transportarray. The lamp (housing HG) and energy-dump unit E-D are mounted on arelated bifurcated casting FC which is affixed (bolted) to the maincasting M-C but under BP. On (or in) main casting M-C are mounted thecomponents making-up both (Front, Rear) "illumination paths" and both"image-lift paths" as described above. A parallelogram-shaped castingP-C, open at both ends, contains the illumination-beam splitter 2-3associated corner mirror 2-5 (FIG. 27) as an integral modular unit, andis attached to MC. Tower-castings T-C, T-C' (e.g. see FIG. 9A, notemachine cover ccv. raised) for each side of the document, eachincorporate a 45° image mirror 3-1, 3-1' (FIGS. 16, 32, 27), anassociated rotatable trunnion mirror 3-3, 3-3' and a photopic filter3-7, 3-7'. The image lenses 3-5, 3-5' and respective two CCPDs (each ona circuit board) are attached on a wall of main casting M-C.

FIG. 27A shows casting MC, with one optical Tower casting mountedthereon, placed within frame CR of the document processor 1-11, on apair of extensible rails Tw, Tw' (partly extended). FIG. 27B is a sideview, showing the rails Tw, Tw' almost-fully extended, with transportbase-plate BP pivoted up. FIG. 27C is an enlarged view of FIG. 27B, withup-tilted base-plate BP and part of casting MC shown in more detail(e.g. note the two casting "coupling-turrets" MC-B1, MC-B2; these, plusa third, MC-B3, will be understood as fitting just under base-plate BPwhen the casting MC is rolled-into Processor 1-11 on its rails Tw, Tw',and the baseplate is dropped into working position--so that three (3)bolts into MC-B-1, -2, -3 can detachably connect MC firmly to BP.)

In conclusion, it will be understood that the preferred embodimentsdescribed herein are only exemplary, and that the invention is capableof many modifications and variations in construction, arrangement anduse without departing from the spirt of the claims.

For example, the means and methods disclosed herein are also applicableto other related document imaging systems. Also, the present inventionis applicable for enhancing other forms of imaging and related opticalarrangements.

The above examples of possible variations of the present invention aremerely illustrative. Accordingly, the present invention is to beconsidered as including all possible modifications and variations comingwithin the scope of the invention as defined by the appended claims.

What is claimed is:
 1. A document-imaging arrangement including twodocument-imaging stations, one for the Front, one for the Rear of thedocuments; illumination-means including stable wavelength "Source meanswith an associated pair of like optical illumination-path arrays; onefor Front illumination, one for Rear illumination; image-lift meansincluding electronic Camera means; and an associated optical image-patharray;said image-path array including photopic filter means adapted toshift the received spectrum in the direction of optimal human-eyeresponse; said Camera means being selected and operated to exhibit aspectral response close to that of the human eye, each said Camera meanscomprising "charge-coupled photo-diode" means CCPD; the beam from saidSource means being split and sent to illuminate the Front and the Rearof each document advanced past said stations; with one for Frontillumination, one for Rear illumination; each said illumination-patharray conducting one of the beams so split to a respective Front or Rearside of the documents; and wherein each said path array further splitsits illumination beam into two like sub-beams, these being directed tofocus at a prescribed point, but being disposed at opposing, equalangles about this point.
 2. The arrangement of claim 1 where each saidstation comprises illumination-shaping slit means; the slit means beingoffset from one another sufficient to effectively avoid interferencebetween Front and Rear illumination.
 3. The arrangement of the claim 2wherein each of the sub-beam pairs are offset about ±30° from the Normalto the documents.
 4. A method of lifting check-images from the front andrear sides of checks as they pass respective offset front and reardocument-imaging stations using illumination-means including stablewavelength source means with an associated pair of like front and rearoptical illumination-path arrays; and operatively associated image-liftmeans including electronic camera means with associated opticalimage-path array; said method comprising:providing filter means, in thisimage-path array, said filter means being selected and adapted to shiftthe received spectrum in the direction of optimal human-eye response;selecting and arranging said camera means to exhibit a spectral responseclose to that of the human eye; splitting the illumination beam fromsaid source means into a pair of sub-beams at the Front and a pair ofsub-beams at the Rear of each document advanced past said stations; eachsaid pair of illumination sub-beams being directed to focus at aprescribed respective point, while also being disposed at opposing,oblique equal angles about this point.
 5. The method of claim 4 whereeach said station is arranged to include illumination-shaping slitmeans; the two slit means being offset from one another, sufficient toeffectively avoid interference between Front and Rear illumination. 6.The method of claim 5 wherein each of the sub-beam pairs are offsetabout ±30° from the Normal to the documents.
 7. Apparatus for liftingcheck-images from the front and rear sides of checks as they passrespective offset front and rear document-imaging stations usingillumination-means including stable wavelength source means with anassociated pair of like front and rear optical illumination-path arrays;and operatively associated image-lift means including electronic camerameans with associated optical image-path array; said apparatuscomprising:filter means disposed in this image-path array, said filtermeans being adapted to shift the received spectrum in the direction ofoptimal human-eye response; said camera means being selected andarranged to exhibit a spectral response close to that of the human eye;the illumination beam from said source means being split into a pair ofsub-beams at the Front and a pair of sub-beams at the Rear of eachdocument advanced past said stations; each said pair of illuminationsub-beams being directed to focus at a prescribed respective point,while also being disposed at opposing, oblique equal angles about thispoint.